The present invention relates to a kitchen apparatus which simultaneously filters grease and airborne particulate matter from hot fumes and transfers heat to a fluid circulating inside the system. An improved piping configuration is disclosed which circulates fluid in parallel through a plurality of heat exchangers and which utilizes a recirculation pump for optimized performance during time periods when there is no demand for hot water from the hot water heater.
During the operation of commercial or institutional kitchens, a significant amount of valuable thermal energy is lost as a result of hot fumes being vented to the atmosphere. These hot fumes are generated from cook stoves, hot plates, deep fat fryers, and other cooking apparatus. As a result of the extreme heat and various fumes generated during cooking, it is necessary for the comfort and health of kitchen workers to exhaust these fumes on a continuous basis through flue chimneys or similar venting devices. This process effectively replaces the hot kitchen air with cooler, clean outside air. Although this circulation process is necessary to provide a constant source of clean air to the kitchen environment, this venting practice is both inefficient and uneconomical, especially in colder climates where the cost to heat internal air and water is significant.
A further problem encountered in commercial kitchens is the filtering of grease and other particulate matter entrained in the hot fumes generated during the cooking of foods. If improperly filtered, this grease can cause fouling and the eventual malfunction of air ventilation systems, as well as create fire hazards if allowed to accumulate. Accordingly, hot fume air filters, which are normally located in fume hoods over cooking surfaces, are generally required to be cleaned daily, or at a minimum of 2-3 times a week. This tedious cleaning process is both time consuming and expensive.
The use of heat exchangers to capture thermal energy above cooking surfaces has been known for years. These designs, however, position the heat exchangers substantially downstream of existing grease filters. This approach is unfavorable for at least three reasons. First, these designs are inefficient since the heat exchanger is located downstream of the grease filter and a significant distance from the heat source. Thus, valuable thermal energy is lost by absorption into the grease filter and through general dissipation prior to the heat reaching the exchanger. Second, the grease filters currently being used upstream of the heat exchangers impede air flow, especially when congested with grease, hence reducing the efficiency of the air ventilation system and heat transfer efficiency. Third, when the heat source is turned off, the grease quickly solidifies on the filters and requires cleaning for both safety and efficiency. Finally, despite the existence of these kinds of heat exchangers generally, many existing kitchens fail to incorporate any kind of heat exchanger. Retrofitting existing kitchen equipment with heat exchanger systems may require an entirely new flue hood assembly and substantial piping and accessories. This conversion is both time consuming and expensive.
Accordingly, it would be advantageous to provide a substantially self cleaning filter which is capable of filtering grease and other particulate matter from hot vapors and fumes generated during the cooking of foods. It would additionally be advantageous to transfer heat from the hot cooking fumes to a fluid passing internally through or substantially adjacent to the filter. This fluid could in turn be used to heat air, water or other fluids for a variety of subsequent uses. By combining the heat exchanger and grease filter into one integral component, the transfer of thermal energy would be more efficient since the heat exchanger is located closer to the heat source. Furthermore, the fluid within the filter would retain heat after the heat source is turned off, allowing the grease to melt and drain away, thus reducing the frequency of cleanings. It would additionally be advantageous to provide a novel baffle design which may be used either independently or in conjunction with the heat exchanger/filter to provide additional filtering of the grease and particulate matter. This baffle design would be significantly more efficient than filters found in the prior art based on the creation of rotational and/or vortex currents as the hot fumes, grease and particulate matter flow through the baffle filter. The combined heat exchanger/filter would further be designed to replace existing grease filters, and thus could be retrofitted easily and at low cost without the need for new flue hood assemblies. One system which provides a heat exchanger used in a kitchen environment is provided in U.S. Pat. No. 5,687,707.
An additional problem associated with the use of heat exchangers used in conjunction with kitchen ventilation systems is the piping and circulation of the fluid through the heat exchangers. More specifically, the fluid is typically circulated through the heat exchangers in series, wherein the energy transfer in each succeeding downstream filter is reduced since the incoming fluid temperature is higher than the fluid temperature in the preceding heat exchanger. Thus, the differential is less in each successive heat exchanger positioned in series. Furthermore, in these types of piping configurations only a minimum amount of fluid can be circulated through the heat exchangers based on the limitations of the piping diameter used in the filters and incoming and outgoing piping. Thus, the maximum amount of heat energy is not collected in the fluid as it is circulated through the heat exchangers.
Another typical problem associated with piping assemblies used in conjunction with heat exchangers in kitchen environments is that there is no apparatus or method for continually recirculating and heating the fluid when there is no demand for heated water. Thus, when there is no demand on the hot water heater, the fluid is not continually circulated through the heat exchangers to capture the thermal energy being emitted from a cook stove or other cooking apparatus. Thus valuable heat energy is lost and not captured for future use in the kitchen environment.
The proposed combination heat exchanger/filter provides means for both filtering grease and particulate matter entrained in cooking fumes, and capturing thermal energy in a fluid circulated throughout the filter. The fluid can then be utilized to transfer heat to a fluid, e.g., water or air.
In a preferred embodiment, the combination heat exchanger/filter can be advantageously employed designed to replace existing grease filters installed in flue hoods in commercial or institutional kitchens. By utilizing quick release hydraulic couplings, the combination heat exchanger/filter may quickly be assembled to fit existing flue hoods by simply replacing the old grease filter and by supplying fluid access and removal. Thus, significant energy savings can be accomplished by replacing an existing grease filter with a combination heat exchanger/filter, eliminating the need for purchasing an entirely new flue hood assembly. The retrofitting is thus fast, inexpensive, and enhances energy efficiency.
By combining the heat exchanger and air filter, a number of significant advantages are realized. First, the heat transfer efficiency between the heat source and fluid circulated within the filter is improved. This is a result of the close proximity between the heat source and heat exchanger when compared to currently existing systems, where the heat exchanger is located downstream of the grease filter and a significant distance from the heat source. As used herein, xe2x80x9cupstreamxe2x80x9d shall be defined as the side closest to the heat source, e.g., cook stove or hot plate, while xe2x80x9cdownstreamxe2x80x9d shall be the side closest to the flue hood chimney. Further, by circulating a cool fluid, such as water in close proximity to the heat source, heat is removed more quickly from the cooking line, thus lowering the surrounding ambient temperature. Additionally, the fluid within the filter can retain heat for a sustained period of time after the heat source is turned off. Thus, by maintaining the fluid temperature at 20-30xc2x0 F. above the melting point of grease with a thermocouple or other temperature control device, the grease will continue to melt and self-drain, even after the heat source is turned off. This self-draining reduces the need for frequent cleanings of the grease filter. Further, by combining the filter and heat exchanger, the air flow through the flue hood ventilation system is improved since there is less resistance from grease solidifying on the filter and impeding air flow prior to reaching the heat transfer mechanism.
In another aspect of the present invention a piping and manifold assembly is provided to optimize the efficiency of heat transfer from the cooking unit to the fluid circulated through the plurality of heat exchangers positioned above the heat generating source. More specifically, an inlet manifold is provided upstream from a plurality of heat exchangers positioned over a heat generating cook stove. The inlet manifold is interconnected to a typical fluid supply source such as fresh water from a typical municipality. The inlet manifold has a plurality of exit ports which generally correspond to the number of heat exchangers positioned in the ventilation hood directly above a cook stove. Likewise, an outlet manifold is positioned downstream of the plurality of heat exchangers and contains a plurality of inlet ports corresponding to the number of heat exchangers positioned over the cooking source. A plurality of service lines interconnects the inlet manifold, outlet manifold and the heat exchangers positioned therebetween in a parallel orientation. The outlet manifold additionally has an outlet end which is interconnected to a hot water heater via a service pipe.
The present invention provides significant advantages over piping assemblies with water circulating in series through the heat exchangers. These benefits include a greater total throughput of water and improved efficiency since the temperature differential of the incoming fluid entering the heat exchangers is typically greater than conventional systems where the water is circulated in series through a plurality of heat exchangers.
In a preferred embodiment of the present invention a recirculation tank is positioned between the outlet port of the outlet manifold and the hot water heater. The recirculation tank outlet end is interconnected to a recirculation line which is in communication with the inlet manifold via the water supply line. A pump is additionally positioned immediately upstream from the inlet manifold to provide sufficient pressure to circulate the fluid in a continuous loop through the plurality of heat exchangers. When there is no demand for hot water, the pressure in the recirculation tank increases until a predetermined pressure level is obtained which activates a signal to turn on the pump. When the pump is operating, the fluid repeatedly recirculates through the heat exchangers, thus continually heating the fluid until there is a demand for hot water. As hot water is drawn from the hot water heater, the pressure in the recirculation tank is reduced below a predetermined pressure setting and the pump is deactivated. The hot water which has been circulating in the plurality of heat exchangers is then passed directly through the recirculation tank and into the hot water heater for use in the kitchen or restaurant environment.